The present invention relates to an optical fiber connector used for connection of optical fibers; and more specifically to a positioning mechanism for matching deviating direction, in the ferrules of optical fibers to be connected, so as to reduce optical coupling loss due to deviation of optical fibers being fixed to the ferrules.
An optical fiber is generally inserted into a ferrule and is fixed therein with a bonding agent such as epoxy resin. FIG. 1A illustrates an enlarged end face of a ferrule, the diameter of ferrul 100 is larger than the optical fiber diameter (102 is core, 101 is clad). Therefore, it is difficult to accurately position the optical fiber in the center P of ferrule 100. As a consequence, it is inevitably fixed in the ferrule 100 with a deviation from the center P of ferrule 100.
Accordingly, in the case of an optical fiber connector where the optical fibers are optically coupled by polishing the end faces of ferrules in a spherical form and then arranging them to abut each other, if the end faces of ferrules are only arranged to abut each other, the cores 102 will not be aligned. This misalignment (such as shown in FIG. 1B) increases the loss in an optical connector.
This problem can be solved by detecting the deviation direction (e.g., the Y direction in FIG. 1A) of the optical fiber core 102 and matching the deviation direction of the optical fiber core 102 in respective ferrules.
Referring to FIG. 1B, optical coupling efficiency can be improved by causing the optical fibers in the right and left ferrules to abut each other in such a manner that the right or left ferrule is rotated 180 degrees.
For this reason, an optical connector positioning mechanism is used so as to cause the deviating direction of cores of the optical fibers in the respective ferrules to be aligned. Such mechanism is explained with reference to FIGS. 2, 3, and 4.
FIGS. 3A, B, C illustrate a conventional optical connector adapter. In this adapter, an elastic sleeve 11 holds the respective ferrules and is floatingly supported within a cylindrical hole 12 by a pair of housings with flanges 13, 13' which are provided with the threadings 10, 10'. These threadings respectively engage a coupling nut 7 (FIG. 2) of a plug. The ferrule 3 of the plug is inserted into the elastic sleeve 11. The end part of a cylindrical material 6 holds the ferrule 3 and fits in a recessed part 14, 14' (FIG. 3B) of the flanges 13, 13'. When the plugs are inserted into the adapters 13, 13' and the respective coupling nuts 7 on the plugs are engaged with the threadings 10, 10' of the adapters 13, 13', the end faces of ferrules 3 are arranged to abut each other and to be fixed within the elastic sleeve 11. A specified pressing force is applied by a spring. 4.
FIG. 2 is a partial cut-away perspective view illustrating a conventional plug of an optical connector. In this plug, the ferrule 3 holds an optical fiber 2, which extends from the optical fiber cord 1 and is held, together with a pressing spring 4, by a plug body 5 and a cylindrical member 6 which threadingly engages the plug body. The ferrule is coupled to the adapter shown in FIG. 3 with the coupling nut 7. The ferrule 3 is mounted loosely in the axial direction of the cylindrical member 6 but is fixed in the rotating direction.
Referring to FIG. 4, in the ferrule positioning structure, the cylindrical member 6, which holds the ferrule, has a groove 16 formed in the circumferential direction and a plurality of grooves 17 in the axial direction extending from groove 16 toward the rear of the cylindrical member 6. A C-ring 30 has pawls 18 which engage the grooves 17, and a positioning pawl 19 for positioning within the adapter shown in FIGS. 3A-3C. The C-ring 30 engages the circumferential groove 16 of said cylindrical member 6. The position of pawl 19 can be adjusted by adequate engagement of pawls 18 with the grooves 17.
The positioning pawl 19 engages the positioning grooves 15, 15' (FIG. 3A) of the adapters 13, 13'. In this structure, a pair of ferrules is arranged to abutting. However, the optical fiber cores are made to deviate in the same direction by adjusting the deviation direction of the optical fiber cores so that they match. The position of the positioning pawl 19 with respect to the deviation direction can be adjusted as follows. Namely, a reference plug in which the deviating direction of the optical fiber core is known is inserted into one side of an adapter and the plug to be adjusted is inserted into the other side of the adapter. Thereafter engagement of pawls 18 within grooves 17 is determined by rotating the C-ring 30 so that the attenuation loss of optical signal is minimized. Because the coupling condition between the positioning pawl 19 and adapter positioning groove 15 is fixed the optical fiber cores in the ferrules will always deviate in the direction set as a result of the above adjustment.
However, the positioning mechanism of the conventional optical fiber connector has following disadvantage. Adjustment (rotation of the C-ring 30) is carried out after shifting the coupling nut 7 in the direction of arrow A in FIG. 2. But, in this case the pawls 18 are hidden by the coupling nut 7. Because the amount that the coupling nut 7 can be shifted is limited, operation of the coupler is difficult and awkward and pawls 18 may be deformed due to excessive force being applied to the pawls 18 during such operation.